Interference effects, fluorescence spectroscopy

The monochromator for x-ray fluorescence spectroscopy is called the analyzing crystal. It differs from all the monochromators described earlier for all the other optical analytical instruments. The effect used in this type of monochromator is not diffraction, but interference. The wavelength of the analyzing light is changed by rotation of the analyzing crystal by certain angle. 

Chemical interference effects in atomic fluorescence are similar to those observed in atomic absorption spectroscopy. In addition, any process that affects the quantum efficiency of the fluorescence or disrupts normal emission of the energy of the excited state also can be considered as a chemical interference. 

Another aspect of optical pumping is related to the coherent excitation of two or more molecular levels. This means that the optical excitation produces definite phase relations between the wave functions of these levels. This leads to interference effects, which influence the spatial distribution and the time dependence of the laser-induced fluorescence. This subject of coherent spectroscopy is covered in Chap. 7. 

In a very early report of direct determination of stabilisers in polymers by luminescence techniques by Drushel et al. [13] the fluorescence of EPR/Age Rite D (trimethyldihydroquinoline) and of EPR/Santonox R were examined. Lack of interference by other polymer additives and polymerisation catalyst residues was emphasised. Age Rite D concentrations can be measured directly in pressed EPR films (<0.01 cm thickness) by fluorescence at levels below 0.1-0.2 wt.% in order to prevent concentration quenching. In the fluorescence emission spectra of Irgafos 168 the fluorescence quantum yield of the phosphate is much greater than that of the phosphite [516]. This difference enables quantification of the phosphate concentration. Although direct quantitative determination of UV stabilisers in extruded polyolefins by means of fluorescence spectroscopy (ex, 370 nm em, 390-550 nm) has been described [517], this is certainly not a universally applicable technique (being additive and matrix dependent). The effects of additives (AOs and cross-linking agent by-products) on electroluminescence... 

In atomic spectroscopy, absorption, emission, or fluorescence from gaseous atoms is measured. Liquids may be atomized by a plasma, a furnace, or a flame. Flame temperatures are usually in the range 2 300-3 400 K. The choice of fuel and oxidant determines the temperature of the flame and affects the extent of spectral, chemical, or ionization interference that will be encountered. Temperature instability affects atomization in atomic absorption and has an even larger effect on atomic emission, because the excited-state popula-... 

Raman spectroscopy has been widely used to study the composition and molecular structure of polymers [100, 101, 102, 103, 104]. Assessment of conformation, tacticity, orientation, chain bonds and crystallinity bands are quite well established. However, some difficulties have been found when analysing Raman data since the band intensities depend upon several factors, such as laser power and sample and instrument alignment, which are not dependent on the sample chemical properties. Raman spectra may show a non-linear base line to fluorescence (or incandescence in near infrared excited Raman spectra). Fluorescence is a strong light emission, which interferes with or totally swaps the weak Raman signal. It is therefore necessary to remove the effects of these variables. Several methods and mathematical artefacts have been used in order to remove the effects of fluorescence on the spectra [105, 106, 107]. 

In conclusion, the most important advantages of FT-MIR spectroscopy to be used in biopolymer characterizations are the spectra can be obtained instantly in a solid form, liquid form, and in different solutions, the sample aliquots are small (less than 1 g), the operation of the equipment is simple, cheap, and the interpretation is done due to data processing software attached to instruments. No light scattering or fluorescent effects may interfere. "... 

Several methods are available for the determination of total aluminum in biological and other materials. Chemical and physicochemical methods are in most practical situations insensitive and inaccurate X-ray fluorescence is specific but lacks sensitivity neutron activation analysis is complex and subject to interferences, although it is a very sensitive technique. Nuclear magnetic resonance spectroscopy is not very sensitive but useful to get information on speciation [33]. Graphite furnace atomic absorption spectrometry (GFAAS) is the most widely used technique and can produce reliable results, provided that the matrix effects are recognized and corrected. Savory and Wills [19] reviewed chemical and physicochemical methods for the determination of aluminum in biological materials, e.g. X-ray fluorescence, neutron activation analysis, atomic emission spectrometry, flame emission, inductively coupled plasma emission spectroscopy, and AAS. 

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